Reactions that employ photocatalysts to degrade organic matter are widely known and industrially used in many fields.
It is common knowledge that, among photocatalysts, titanium dioxide in particular, when exposed to ultraviolet light, generates active oxygen which is very strong oxidant, thereby decomposing organic compounds adhering to the catalyst and exhibiting bactericidal effects.
A variety of commercial products which make use of this quality of titanium dioxide for such purposes as to prevent soiling, suppress microbial activity, deodorize, purify water, and purify air have already been developed.
At the same time, in connection with the degradation of harmful substances, active research is being done on the efficient photolysis of chemical substances, including dioxins and other halogen-containing compounds, environmental hormones and dyes, within solvents using titanium dioxide as the photocatalyst. For example, sewage and wastewater treatment systems that use this degradation reaction have been developed (see Patent Document 1: JP-A 10-337579; Patent Document 2: JP-A 11-290840; Patent Document 3: JP-A 2000-93951; Patent Document 4: JP-A 2000-354863; Patent Document 5: JP-A 2000-202468; Patent Document 6: JP-A 2001-327961).
Generally, most of these wastewater treatment processes are carried out in water. However, one drawback has been the slow rate at which the degradation reaction proceeds. Also, because such wastewater treatment processes are carried out with the photocatalyst suspended in water, removal and recovery of the catalyst is difficult. Complex operations are required to improve the removal and recovery ratios of the catalyst.
Patent Document 1: JP-A 10-337579
Patent Document 2: JP-A 11-290840
Patent Document 3: JP-A 2000-93951
Patent Document 4: JP-A 2000-354863
Patent Document 5: JP-A 2000-202468
Patent Document 6: JP-A 2001-327961